The present invention relates to a gas-venting arrangement incorporated with a mold for use in a molding machine, such as a die casting machine or an injection molding machine.
The die casting method has heretofore been used widely as the molding method for manufacturing large quantities of precision products. However, this method is often unsuitable for preparing high quality products for which the absence of voids in the interior of the product is required. The reason is that since a molten metal or melt is injected at a high speed under a high pressure into the mold cavity, gases are not sufficiently vented from the mold cavity but are mingled with the molten metal therein and often left in the product. As means for overcoming the above-mentioned disadvantage, there has been proposed a pore-free die casting method in which the atmosphere of the interior of the mold cavity is replaced by an active gas and the active gas is combined with the molten metal, and thus stabilized, or a method in which the pressure is reduced. These methods, however, cannot ordinarily be adopted.
The inventors examined the relation between the area of the air vent from the mold cavity and the value of the specific gravity of the cast product in a model die casting machine, and it was found that the value of the specific gravity of the cast product increase with an increase in the area of the air vent. However, the number of air vents is limited by the size of the cast product, and in order to prevent the molten metal from passing through the air vent, it is not allowable to increase the diameter of the air vent beyond about 0.1 mm.
It is, therefore, a primary object of the present invention to provide a gas-venting arrangement incorporated with a mold, in which a large quantity of gases can be vented despite the above-mentioned limitations of the size of the cast product or the structure of the mold, and a high quality product can be obtained while preventing inclusion of the gases therein, which inclusion would cause formation of voids in the product.
Another object of the present invention is to provide a gas-venting arrangement incorporated with a mold overcoming the above-mentioned disadvantages, which has a simple construction and serves the function of discharging gases smoothly from the mold during a die casting or injection operation, while the amount of molten metal forced to flow out of the mold cavity is drastically reduced.
According to the present invention, there is provided a gas-venting arrangement incorporated with a mold for use in a die casting machine or an injection mold machine. The mold consists of stationary and movable mold halves, both defining a cavity to be filed with a molten metal. The gas-venting arrangement comprises: a gas vent passage formed in the mold to communicate with the cavity; at least one by-pass passage branched from the gas vent passage, formed in the mold; a gas discharge passage formed in the mold to communicate with the outside of the mold; and valve means, including a movable valve confronting the gas vent passage and a valve chamber having a valve seat formed in the mold, for opening and closing the gas vent passage, the by-pass passage, and the gas discharge passage in such a manner that the valve cooperates with the valve chamber to prevent the gas vent passage from communicating with the gas discharge passage, while allowing the by-pass passage to communicate with the gas discharge passage when the valve is in a first position within the valve chamber, and to prevent the by-pass passage and the gas vent passage from communicating with the gas discharge passage when the valve is in a second position within the valve chamber. The by-pass passage is designed as a detour from the gas vent passage to the valve chamber. In the above arrangement, the valve is forced to move from the first position to the second position by a part of the melt forced to flow out of the cavity and through the gas vent passage upon impingement of the melt part against the valve, before a part of the melt part flowing through the by-pass passage reaches the valve chamber. The cavity, the gas vent passage, the by-pass passage, and at least a forward portion of the valve chamber communicating with the gas vent passage have cross-sections which are parallel to the axis of the mold, the shape of each cross-section being defined by both mold halves. Preferably, the gas-venting arrangement further comprises means for elastically urging the valve against the mold so that the valve is maintained in the first position before the impingement of the melt against the valve. The valve means and the urging means may be located so that they have a common axis perpendicular to the axis of the mold. Alternatively, they have a common axis parallel to the axis of the mold. In both cases, preferably the gas vent passage and the by-pass passage may lie on a plane perpendicular to the axis of the mold.
With respect to the movement of the movable valve, the valve may be mounted in the valve chamber for axial movement and the valve means may be designed so that the valve slidably moves from the first position to the second position along the axis of the valve chamber. Alternatively, the valve may be pivoted so as to rotate about a pivotal axis and the valve means may be designed so that the valve is rotated from the first position to the second position.
The gas-venting arrangement is preferably provided with a hydraulic cylinder for actuating a piston which is connected to the valve means or the urging means so that the valve or the urging means is moved with the piston as needed.
A gas evacuation means such as a suction cylinder or vacuum tank is preferably provided in such an arrangement so that an inlet of the evacuation means communicates with the outlet of the gas discharge passage. The operation of the evacuation means may be synchronized with the injection operation.